This invention relates to a numerical control apparatus for an NC machine tool which performs C-axis machining.
A numerical control apparatus ordinarily is adapted to execute numerical control processing based on NC program data, and to control an NC machine tool such as a lathe in accordance with the results of processing to subject a workpiece to machining specified by a command. Recent numerical control apparatus come equipped with subprogram and custom macro functions through which various complicated machining control programs and repetitive control programs can be prepared in a simple manner.
The aforementioned custom macro is utilized in order to comply with a user request that the NC machine tool be provided with the function of a lead processing machine in a case where C-axis machining is to be performed. However, this makes it necessary that the machining command data be supplied to each axis at a rate greater than the conventional distribution frequency. In other words, a lead machining function refers to a machining function in which, in an NC machine tool having a mechanical construction of the kind shown in FIG. 7, a tool t on a Z axis parallel to the rotational axis C of a workpiece w is moved at high speed along the Y axis by a move command independent of the Z axis to subject the workpiece w to milling. Such a lead machining function is essential in the machining of e.g. the head of a video deck, which requires that the workpiece w be rotated and that the movement of the tool be controlled in such a manner that the amount of machining differs every rotational angle during one revolution of the workpiece. In a machine tool for practicing this lead machining, it is also necessary to deal not only with lead machining but also with ordinary milling by the tool t in accordance with the drive axes X, Z of the tool t. With the conventional numerical control apparatus, the preparation of the amount of high-speed distribution data necessary for lead machining and the editing of programs cannot be performed in a simple manner, and special-purpose machinery is required for this type of machining.